مقدار الوزن الذرّي يحدّد طبيعة العنصر، كما يحدّد مقدار الجزيء طبيعة الجسم المركّب.

“The magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body.”Dmitri Mendeleev — Mendeleev on the Periodic Law: Selected Writings, 1869 - 1905 (2013)